The present invention relates generally to the field of image forming devices and in particular to a media sensor for sensing and distinguishing between no media, opaque media, and transparent media.
To ensure high quality image formation, precise control of the speed and position of media sheets is required as they are transported within an image forming apparatus, for example, to ensure accurate registration of various color plane images applied separately to the media sheet. In addition, many parameters of the image-forming process, such as the media sheet transfer speed, the operating temperature of a fuser, and the like, depend on the type of media. For example, opaque media such as bond paper may require different image formation and fixing parameters than other media, such as transparencies. Hence, it is critical that both the position and the type of media sheet (e.g., opaque sheet or transparency) be accurately sensed.
A wide variety of media sensors are known in the art. In general, a media sensor may comprise an electro-mechanical contact that is made or broken when a media sheet trips a mechanical lever disposed in the media sheet path; an optical sensor whereby a media sheet blocks, attenuates, or reflects optical energy from an optical source to an optical detector; an opto-mechanical sensor, or other sensor technology, as well known in the art.
In practice, a given image forming apparatus may employ a plurality of media sensors. For example, two or more media sensors may be arrayed across the media path in a direction perpendicular to the media sheet transfer direction, to detect the media sheet width. As another example, many image-forming devices employ a first sensor to detect the position of a media sheet, and a second sensor to detect its type (e.g., opaque sheet or transparency). Both cost reduction and improved system reliability may be obtained by combining the functions of a plurality of sensors into a single, compact, integrated media sensor capable of sensing both the position and type of media sheets.